In recent years, a technique for achieving a white light-emitting device has been widely used, in which a fluorescent material like YAG (yttrium aluminum garnet) phosphor is placed in the vicinity of a blue LED (Light-Emitting Diode) chip based on gallium nitride (GaN). In such a white light-emitting device, white light is created as a color mixed of the blue light emitted by the blue LED chip with the yellow light emitted in secondary emission by the phosphor, which has received the blue light. In addition, another type of technique for generating white light as a mixed color is also employed in which the blue light emitted by the blue LED chip is mixed with the red light and the green light that are emitted as secondary emission by phosphors of the respective colors, in receipt of the blue light.
Such a white light-emitting device has various applications. For example, there is a demand that the device be used as replacements for fluorescent lights and incandescent lamps. Such application is now further extending to lighting devices like headlights for automobiles, which require very high brightness.